Many industrial fields require laser processing capability and for such applications, the primary concern is often to generate optical laser pulses with, to some extent, real-time control over the pulse amplitude, duration, shape, peak power and repetition rate. In some applications, such as laser-based material-processing, the rise time and fall time of the shaped optical pulses are also important functional specifications.
U.S. Pat. No. 7,348,516 (SUN et al.), entitled “Methods of and laser systems for link processing using laser pulses with specially tailored power profiles” presents many arguments in favor of pulsed laser systems providing fine control over the pulse temporal power profile in the nanosecond regime, for facilitating better link process quality and yield. Three different laser architectures providing a certain control over the laser pulse shapes are described therein. U.S. Pat. No. 7,126,746 (SUN et al.) further teaches a laser system providing control over the pulse shapes and having a Master Oscillator Power Amplifier (MOPA) configuration. A practical manner of digitally generating appropriate control signals for such systems is not however described in either document.
U.S. Pat. No. 6,281,471 (SMART), entitled “Energy-efficient, laser-based method and system for processing target material” describes many requirements and specifications concerning the temporal generation of square laser pulse shapes in material processing. The system presented therein includes, among its main components, a controller for generating a processing control signal, and a signal generator for generating a modulated drive waveform based on the processing control signal. SMART however does not tackle the issue of the implementation or integration of the controller and the waveform generator into the system described.
Optical pulse shaping implementation can originate from digital electronic means, where some electronic apparatus reads a given sequence of digital samples previously stored in a memory buffer, and writes these samples into a digital-to-analog converter (DAC). The shaped analog signal output by the DAC is then fed to a buffer amplifier having enough bandwidth and drive capability for directly modulating a light source such as a laser diode, or driving an electro-optic modulator.
U.S. Patent Application Publication No. 2008/0080,570 (MURISON et al.), entitled “Method and system for a pulsed laser source emitting shaped optical waveforms” presents a tunable pulsed laser source where optical pulse shaping is based on the digital approach just described above. This pulsed laser architecture implements a double-pass optical fibre amplifier that uses a single Mach-Zehnder type amplitude modulator. The electrical analog shaping signal drives two successive openings of the optical modulator. MURISON also emphasized that electrical pulse shaping capability is beneficial for the reduction of gain saturation in the fiber amplifier, or for several fields of laser processing where it is desirable that the optical pulse be different than a square pulse. Although MURISON mentions that the shaped waveform originates from a digital pattern stored in memory on-board a DAC, it does not provide an explicit architecture or method for transferring data from the memory to the DAC, apart from using built-in functional features of an off-the-shelf laboratory instrument such as the AWG2040 (trademark) waveform generator from Tektronix Inc.
Other architectures than the one described by MURISON exist for building pulsed laser sources and these architectures may benefit from the advantages of optical pulse shaping produced from digital electronics as well. An example is U.S. Pat Application published under No. US2006/0159138 (DELADURANTAYE et al.), entitled “Pulse laser light source”. This patent application describes a pulse laser source built around two Mach-Zehnder modulators. In the general case of this architecture, it is likely that distinct analog pulse shaping signals must be generated for each modulator, along with proper synchronization and delay settings between one and the other.
Finally, pulsed laser sources sometimes necessitate that several utilitarian functions or modes of operations be present in or in close vicinity of the main architectural body of the fiber amplifier. Typical examples of such functions or modes of operations are a bias servo function for maintaining the extinction point of an electro-optic modulator, the on-demand generation of a quasi-CW optical output or the monitoring and control of the laser pump drivers. In those approaches where individual stand-alone waveform generators and controlling electronics are used, timing jitter as well as synchronization aspects must be carefully managed. In general, such approaches result in higher system cost, volume and complexity.
There is therefore a need for a digital module for generating appropriate control signals for a pulsed laser oscillator.